Generally, a plurality of pipes such as ductile cast iron pipes have been connected to constitute a pipeline, for example, a buried pipeline for water supply. If such a pipeline includes a fitting, e.g., a bend, a tee, a reducer, and a plug, an uneven force is applied to a bent portion, a branch portion, or a pipe-diameter changing portion of the fitting (specifically, a point where a water flow direction is changed or a point where the cross-sectional area of a flow channel is changed) so as to move the pipe according to a water pressure in the pipe. A pipe portion in a certain distance range continuing to the point (the bent portion, the branch portion, or the pipe-diameter changing portion of the fitting) is influenced by the uneven force, so as to be moved. Thus, at the joints of fittings, the joints of a fitting and a pipe, and the joints of pipes near the fitting and the pipe, a separation preventive pipe joint is preferably used. The separation preventive pipe joint is configured to deflect pipes at the joint to some extent and has the function of preventing separation between the pipes even under the uneven force.
As shown in FIGS. 3 and 5, such conventional separation preventive pipe joints include metallic annular spigot protrusions 52 and 62 that are formed around the vicinities of the ends of spigots 51 and 61, and metallic lock rings 55 and 65 that are disposed in lock ring storage grooves 54 and 64 formed in sockets 53 and 63. When the spigots 51 and 61 are removed from the sockets 53 and 63, the spigot protrusions 52 and 62 come into contact with the lock rings 55 and 65 from the rears of the sockets 53 and 63, thereby preventing the spigots 51 and 61 from separating from the sockets 53 and 63. Reference numerals 56 and 66 in FIGS. 3 and 5 denote seal members stored in seal member storage grooves 57 and 67 formed in the sockets 53 and 63.
In the conventional separation preventive pipe joint shown in FIG. 3, the metallic lock ring 55 has one slit in its circumference, that is, the lock ring 55 is shaped like a ring having a split at a point in its circumference and is closely fit onto the outer surface of the spigot 51 in the lock ring storage groove 54. In the separation preventive pipe joint shown in FIG. 5, the metallic spigot protrusion 62 considerably protruding in a radial direction is fixed around the end of the spigot 61 with a welded portion 62a. Furthermore, the metallic lock ring 65 having one slit in its circumference is inserted into the lock ring storage groove 64 and is kept with an increased diameter in the lock ring storage groove 64 with a bolt 69 attached to a diameter-increasing auxiliary part 68 from the outside of the socket 63. The separation preventive pipe joint in FIG. 5 is disclosed in U.S. Pat. No. 4,524,505. JP54-106918A discloses a separation preventive pipe joint having a similar structure to that of U.S. Pat. No. 4,524,505.
In the conventional separation preventive pipe joints shown in FIGS. 3 and 5, the lock rings 55 and 65 and the spigot protrusions 52 and 62 are made of non-deformable metallic materials as well as the sockets 53 and 63 and the spigots 51 and 61. If pipes having the separation preventive pipe joints are deflected at the joints of the pipes, as shown in FIGS. 4 and 6, the sockets 53 and 63 and the lock rings 55 and 65 or the lock rings 55 and 65 and the spigot protrusions 52 and 62 come into contact with only a single point in the circumference, that is, in a so-called edge loading state. Thus, in this state, the pipe receives a force applied in a removing direction, e.g., a drawing force generated by a water pressure in the pipe, thereby applying a large stress to the sockets 53 and 63 and the spigots 51 and 61. This may damage the lock rings 55 and 65 and the spigot protrusions 52 and 62 on the contact point or separate the spigot protrusions 52 and 62 from the spigots 51 and 61 so as to remove the spigots 51 and 61 from the sockets 53 and 63. Thus, the conventional separation preventive pipe joints in FIGS. 3 to 6 disadvantageously have a low-level separation preventing function.
JP2008-25715A and JP62-237193A disclose separation preventive pipe joints that can respond to such a low-level separation preventing function. As shown in FIG. 7, in the separation preventive pipe joint disclosed in JP2008-25715A, a socket lock ring 72 and a socket ring 73 are disposed around a socket 71 while a spigot lock ring 75, a spigot protrusion 76 including a weld bead, and a spigot ring 77 are disposed around a spigot 74. The socket ring 73 and the spigot ring 77 are connected via a bolt 78 and a nut 79.
As shown in FIG. 8, even when the separation preventive pipe joint is deflected, the connecting length of the bolt 78 and the nut 79 is adjusted so as to have an adjusted distance between the socket ring 73 and the spigot ring 77. This can satisfactorily bring the socket 71, the socket lock ring 72, and the socket ring 73 into contact with one another over the circumference without edge loading and bring the spigot ring 77, the spigot lock ring 75, and the spigot protrusion 76 into contact with one another over the circumference without edge loading. Thus, even if a drawing force generated by a water pressure is applied to the pipes, separation between the pipes can be satisfactorily prevented. JP57-165883U and U.S. Pat. No. 4,871,197 also disclose separation preventive pipe joints having similar structures.
As shown in FIG. 9, the separation preventive pipe joint disclosed in JP62-237193A includes an annular holder 83 that protrudes into a lock ring storage groove 82 of a socket 81 from the outside of the socket 81 and comes into contact with a lock ring 87. Multiple small iron balls 84 are stored between the holder 83 and the bottom of the lock ring storage groove 82. In FIG. 9, reference numeral 85 denotes a spigot and reference numeral 86 denotes a spigot protrusion. In the separation preventive pipe joint, the holder 83 is disposed in the socket 81 so as to come into contact with the circumference of the lock ring 87, and then a gap between the holder 83 and the bottom of the lock ring storage groove 82 needs to be completely filled with the small iron balls 84
Also in the separation preventive pipe joint, the gap completely filled with the iron halls 84 brings the holder 83 into contact with the circumference of the lock ring 87. Thus, even if a drawing force generated by a water pressure is applied to pipes so as to deflect the separation preventive pipe joint, as shown in FIG. 10, separation between the pipes can be satisfactorily prevented.